Technical Field
The present disclosure relates to a method and apparatus utilized in wireless communication systems. More particularly, the present disclosure relates to a method and apparatus of handling device to device communication in a wireless communication system.
Description of Related Art
The 3rd Generation Partnership Project (3GPP) has developed a universal mobile telecommunications system (UMTS) which adopts a wideband code division multiple access (WCDMA) as a wireless air interface. In the UMTS, a radio access network known as a universal terrestrial radio access network (UTRAN) includes multiple Node-Bs (NBs) for communicating with multiple user equipments (UEs). The WCDMA provides high frequency spectrum utilization, universal coverage, and high-speed multimedia data transmission which are beneficial for the UEs and the NBs of the UMTS. Furthermore, a long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard is now being developed by the 3GPP as a successor of the UMTS, to further enhance performance of the UMTS to satisfy user's increasing needs. The LTE system includes a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved UTRAN (E-UTRAN) includes multiple envolved NBs (eNBs) for communicating with multiple UEs, and communicates with a core network including a mobility management entity (MME), serving gateway, etc for Non Access Stratum (NAS) control.
An LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
The specification of 3GPP Rel-12 defines that if UEs are in proximity of each other, these devices may be able to use a direct data path to communicate with or discover each other. The UEs which perform this type of communication, i.e., a Proximity-based Service (ProSe) or a device to device (D2D) communication, are said to be in a ProSe communication mode or a UE-to-UE communication mode.